There would also be the question of whether this man was born to citizen parents, and whether Puerto Rico itself is fully subject to the jurisdiction of the US.

He is at least second generation Puerto Rican-born. His parents were even citizens at the time of his birth in 1960. As for your last part, refer to the United States Code:

8 USC § 1402

All persons born in Puerto Rico on or after April 11, 1899, and prior to January 13, 1941, subject to the jurisdiction of the United States, residing on January 13, 1941, in Puerto Rico or other territory over which the United States exercises rights of sovereignty and not citizens of the United States under any other Act, are declared to be citizens of the United States as of January 13, 1941. All persons born in Puerto Rico on or after January 13, 1941, and subject to the jurisdiction of the United States, are citizens of the United States at birth.

There is NO QUESTION except from Birthers for whom there will be no satisfaction.

Too little rigor when dealing with legal terms of art such as “citizen at birth” and “subject to jurisdiction” might lead some to believe that that statute conferred natural born citizenship, which term itself is a legal term of art for a status that cannot be conferred via statute.

It doesn’t say what you’re implying it to say, in other words. Revisit my comments above and understand that it is possible to be born in an unincorporated territory not fully subject to the jurisdiction of the United States.